Sorry to break this to you, but there's probably a good portion of your email list that has lost interest. Neglecting to look at metrics and weed out the disengaged might make you feel good about the size of the list, but there are some long-term negative effects to consider.

We rarely think about pruning the list, but it's pretty important. Continually sending to people who don't open your emails damages your reputation as a sender and is just asking for spam complaints.